The present invention relates to warning light systems for off-highway vehicles, and more particularly to control systems for operating such warning lights.
Occasionally agricultural and construction equipment which is primarily intended for off-road use has to be driven on a highway between work locations. Because these vehicles move at relatively slow speed compared to highway vehicles, hazard warning lights are located at both the front and rear the vehicle. For example the American Society of Agriculture Engineers (ASAE) has promulgated standards which state that self-propelled equipment, for example a farm tractor or combine, have rear and forward facing amber lamps to provide a hazard warning. These lamps flash at a rate of 70 pulses per minute in unison while the equipment is moving in a straight path. The lamps also are utilized as turn indicators in which case the lamps on the side of the equipment in the direction of the turn flash at 100 pulses per minute and the lamps in the direction opposite to the turn are illuminated steadily. The tractor contains a circuitry which governs the operation of these lamps according to this standard.
It is quite common for such self-propelled equipment to pull an implement such as a wagon, manure spreader, hay bailer or other vehicle. The ASAE standards also dictate that the non-self propelled, or towed, vehicles have warning lights at its rear. In particular the towed implement must have a pair of tail lamps as well as left and right amber hazard warning lamps that function in unison with the corresponding hazard warning lamps on the tractor. The power signals for operating these lights on the towed vehicle are supplied through a standard electrical connector on the back of the tractor. The connector provides terminals for the signals from the right and left hazard lamps, tail lights and vehicle ground.
The ASAE standards require that an additional red or amber rear facing lamp be positioned on each side of the vehicle. When the equipment is not turning, the additional red or amber lamps are inactive and during a turn the additional lamps operate unison with the hazard lamps. Specifically the additional lamp on the side of the turn flashes at 100 pulses per minute while the opposite lamp is steadily illuminated. Because these additional lamps must remain inactive when a turn is not occurring, they cannot simply be connected in parallel with the other hazard lamps on the towed vehicle, but must be controlled separately. However, the connection between the tractor and the towed vehicle does not provide additional connection for these lamps. Therefore, control logic must be provided on the towed vehicle to derive signals from the hazard lamp signals in order to drive the turning lamps.
U.S. Pat. No. 5,498,929 describes one type of such control logic which employs a diode-resistor circuit to operate a relay that controls the flow of electricity through the additional turn indicator lamps on the towed vehicle. However, this circuit places the relay in the connection of the lamps to vehicle ground. This precludes the use of standard lamp assemblies on the towed vehicle. Such lamp assemblies have tail lamps, regular hazard warning lamps and the additional turn indicator lamps in a common housing with the grounds for all the lamps connected in common. With this previous control logic, a separate ground connection has to be provided for the additional turn indicator lamps, thereby requiring non-standard lamp assemblies.